(3068) Proposal to conserve the name <i>Polypodium lineare</i> (<i>Dicranopteris linearis</i>) (<i>Gleicheniaceae</i>) with a conserved type

(3068) Polypodium lineare Burm. f., Fl. Indica: 235, t. 67, fig. 2. 1 Mar–6 Apr 1768, nom. cons. prop. Typus: [Sri Lanka], “Ceylan 1773”, “No. 35” (G-PREL barcode G00349562 [ex Herb. Delessert] [image!]), typ. cons. prop. The genus Dicranopteris Bernh. encompasses large erect or scandent ferns often growing abundantly and forming dense thickets in disturbed habitats, e.g., open hillsides, cuttings and forest margins. They are widespread in tropical and subtropical areas of the Old and New World and reach their highest diversity in Malesia (Kramer in Kubitzki, Fam. Gen. Vasc. Pl. 1: 145–152. 1990). The latest comprehensive taxonomic revision of the genus was published by Nakai (in Bull. Natl. Sci. Mus. Tokyo 29: 1–71. 1950) and it is currently considered largely outdated. Current estimates of the number of species of Dicranopteris by various authors range between 12 and about 20 (Kramer, l.c.; PPG I in J. Syst. Evol. 54: 563–603. 2016) with as many as seven new species names added recently (Wei & al. in Frontiers Pl. Sci. (Lausanne) 12-748562: 1–12. 2021; Lima & Salino in Phytotaxa 533: 98–104. 2022). Dicranopteris linearis (Burm. f.) Underw. (in Bull. Torrey Bot. Club 34: 250. 1907) was first described by N.L. Burman as Polypodium lineare (Burman, Fl. Indica: 235. 1768). In the protologue, Burman fil. provided a diagnostic phrase, references to Linnaeus's Flora Zeylanica (p. 201. 1747) and J. Burman's Thesaurus Zeylanicus (p. 97. 1736) and an illustration showing a frond fragment (two branches of the ultimate fork). The distribution area was given by Burman fil. as “Habitat in Java”. In the Burmans’ herbarium (now incorporated in the Delessert Herbarium and deposited at G-PREL), there are four specimens annotated as Polypodium lineare. Three of those (G barcodes G00349562, G00349563, and G00349564) were collected in Sri Lanka (“Ceylan”) in 1773 after the publication of Burman's Flora Indica and thus cannot be considered part of the original material. The fourth specimen (barcode G00360111) was collected in Java by Van Santen. According to the information on one of the attached labels, the specimen was received by the Burmans in 1758. The specimen matches the illustration of P. lineare on t. 67 of Flora Indica so perfectly that there is little doubt that it was used as a model in the preparation of that drawing. Merrill (in Philipp. J. Sci. 19: 336. 1921) stated that “Burman's actual type is a Javan specimen”. As there is a single specimen of P. lineare in the Burmans’ herbarium that was collected in Java, this statement is generally accepted as the first effective lectotypification of P. lineare Burm. f. and Merrill's choice has been followed by the majority of authors (e.g., Nakai, l.c: 65; Pichi-Sermolli in Webbia 17: 33–43. 1962; Mazumdar & al. in Candollea 74: 100. 2019), although an argument could be made that this had already been accomplished by Underwood (l.c.), who commented “type from Java” following his citation of P. lineare Burm. f. However, Holttum (in Van Steenis & Holttum, Fl. Males., ser. 2, 1: 34. 1959) cited the type specimen as “Ceylon, Herb. Delessert (G)”. As mentioned above, Sri Lankan specimens of P. lineare in the Burmans’ herbarium are later additions. They do not belong to the original material and thus Holttum's typification has no standing. Pichi-Sermolli (l.c.) provided a detailed discussion of the lectotype specimen from the Burmans’ herbarium. He noted its large dimensions and lack of hairs. He concluded that the type specimen matched Dicranopteris linearis var. linearis despite those characters being atypical for this taxon. However, Fraser-Jenkins (in Fraser-Jenkins & al., Annot. Checkl. Ind. Pterid. 3: 328–329. 2020) re-identified the lectotype of Polypodium lineare as a specimen of Dicranopteris curranii Copel. (in Philipp. J. Sci. 81: 4. 1952), a more localised Malesian species generally recognized as distinct from D. linearis. The name Dicranopteris linearis (Burm. f.) Underw. is widely used in scientific literature. A search with the query “Dicranopteris linearis” in Google Scholar returned over 5300 hits (search performed on 16 Jan 2025). However, the name had often been used in a broad sense in the past and it is still occasionally misapplied to other Old World species of the genus. The current species concept of D. linearis corresponds to “Dicranopteris linearis var. linearis” as circumscribed by Holttum (l.c.). Even when taken in this narrow sense, D. linearis has the largest distribution range among all species of Dicranopteris. It is widespread in tropical areas of the Old World from West and South Africa and over large areas of South and South-East Asia to Australia and Pacific Islands (Fraser-Jenkins & al., Annot. Checkl. Ind. Pterid. 1: 100–105. 2017). If the name Dicranopteris linearis were to be applied to the taxon currently known as D. curranii, it would have an extensive detrimental effect on nomenclatural stability. The conservation of the name D. linearis with a new conserved type is therefore proposed here. As already noted, the current concept of D. linearis corresponds to Holttum's (l.c.) “D. linearis var. linearis”. Holttum attempted to fix his concept of the type variety of D. linearis by designating a specimen from Sri Lanka as lectotype. Therefore, we find it appropriate to propose a Sri Lankan specimen as the conserved type of D. linearis. Choosing a specimen originating from Sri Lanka as a conserved type has an additional advantage, as there are only two easily recognizable species of Dicranopteris known to occur in Sri Lanka, D. linearis and D. taiwanensis Ching & P.S. Chiu (Fraser-Jenkins & al., l.c. 2017). The specimen from the Burmans’ herbarium (G-PREL, barcode G00349562) is proposed here as a new conserved type of Polypodium lineare. This specimen agrees with the current taxonomic concept of D. linearis (Holttum, l.c.; Tagawa & Iwatsuki in Smitinand & Larsen, Fl. Thail. 3: 50–56. 1979; Chinnock & Bell in Orchard & McCarthy, Fl. Austral. 48: 160–162. 1998; Verdcourt in Beentje & Smith, Fl. Trop. East Afr. (Gleicheniaceae): 6–8. 2000; Shaffer-Fehre in Dassanayake & Clayton, Rev. Handb. Fl. Ceylon 15A: 173–175. 2006; Perrie & Brownsey in Breitwieser & al., Fl. New Zeal. 12: 4–8. 2015; Fraser-Jenkins & al., Ferns Fern-Allies Nepal 1: 127–128. 2015; Fraser-Jenkins & al., l.c. 2017, 2020) and it shows typical long bracts surrounding the apical bud as well as the presence of some hairs on the axes, characteristic for this taxon. Proposed conservation of the name Polypodium lineare would maintain the current use of the name Dicranopteris linearis and in this way contribute to nomenclatural stability. If, however, this proposal is rejected, the name D. linearis is to be applied to the taxon currently known as D. curranii. At the same time, rejection of the proposal might create considerable uncertainty over the earliest name applicable to the taxon currently known as D. linearis.